The simultaneous detection of the fluorescence of marker dyes in a reference and in the sample using an excitation source with 2 distinct illumination wavelengths in the blue-green portion of the visible spectrum is a widely practiced analytical tool. This approach has been used in the most capable automated DNA sequencers, and a number of other biomedical instruments. To achieve this, current machines use either 2 gas lasers with blue and green lines, or 2 lines from an argon ion laser. These laser light sources are bulky, power inefficient, and expensive. A low cost blue-green laser that is compact and provides high output power is highly desirable. Such a device will have a tremendous positive impact on health science related instrument designs. One (1) solution to achieve this aim is the development of a dual wavelength (blue-green) optical fiber lasing cavity based laser source. Such a source has a number of advantages over solid crystal and gas based devices and is considered ideal for developing miniature inexpensive lasers for biomedical applications. Yb-doped optical fiber stands out, in particular, because of its 2 absorption bands. This characteristic shows promise for the development of a dual-line laser. In this project, our overall aim is to develop a double clad single mode Yb-doped fiber based laser emitting at 2 visible lines: blue (489 nm), and green (519 nm). This will be achieved by frequency doubling the primary emission lines of Ytterbium (Yb) at ?=978 nm and ?=1038 nm. In Phase I, we demonstrated the feasibility of generating blue and green lines from Ytterbium-doped fiber. In Phase II, we will fabricate and test a working prototype of the blue-green laser for biomedical applications. In the long term, the commercial availability of this dual wavelength laser light source will enable the creation of automatic DNA sequencers that are much smaller and less expensive than present models, are less costly to operate, and will provide higher sequencing speed and accuracy.